If you had a collision with something 50 times your weight, it would probably (pun intended) have a major impact. But mosquitos do this all the time. Raindrops can weigh 50 times more than a mosquito, yet the animals thrive in rainy and humid areas. For some perspective, imagine walking down the street and suddenly being hit by a mass of water with the weight of a Chevy Suburban.

Fortunately for our collective curiosity, a group of mechanical engineers and biologists from Georgia Tech, led by Professor David Hu, decided to figure out how the pests manage it.

During a thunderstorm, a mosquito would likely be hit about every 25 seconds. They obviously aren’t dodging raindrops, as appealing as the mental image may be.

So the researchers created a “flight arena” to study mosquito-raindrop collisions—essentially a five centimeter wide, 20 centimeter tall rectangular mesh cage. In order to simulate raindrops falling at their terminal velocity (which would otherwise require a height of 10 meters) they shot a water jet point-blank into the cage of mosquitos.

To figure out what was happening during midair collisions, the authors shot a strong, 9m/s jet into the cage, and observed the impact with six mosquitos. In all of these collisions, the insects tumbled down the cage, getting hit repeatedly, before separating from the jet and landing on the side of the cage. This jet is actually stronger than terminal velocity raindrops, so this test shows that mosquitos would survive such an impact.

That didn’t answer the question of how the mosquitos survive a typical impact, so next they used slower and more realistic water drop speeds (10–260 cm/s), which allowed more accurate tracking and higher resolution imaging.

Confirming an earlier prediction, the team found that most drops impacted on the wings and legs, rather than the bodies—the body only makes up one-quarter of the potential impact area. This results in a quick, glancing blow that essentially rotates the insect (either pitch, yaw, or roll). The contact lasts a fraction of a second, after which the mosquito quickly recovers.

But direct hits to the body did happen. When rain falls on a stiff object, like a tree branch, the drops spread out very quickly. This rapid momentum transfer results in a strong impact force, roughly 10,000 times the weight of a mosquito. In other words, splat.

In the experiment, the rarer direct impacts lasted longer and pushed the mosquitos downward several (5–20) body lengths. However, unlike impacts on stiff surfaces, the mosquito and water drop quickly separated—the drop remained intact and retained nearly the same speed. Unless the insect was flying too low to the ground—in which case it would suffer a second, more forceful impact—it was always able to recover.

The key detail is that the raindrops maintain most of their speed after the impact. Transfer of momentum, and therefore impact force, depends on the difference in the drop speed before and after the impact. Compare this to a drop hitting a solid surface: the drop has zero speed after the impact, so all of the momentum was transferred during the collision. The mosquito, on the other hand, just rides along with the raindrop before pulling away safely, much like a surfer riding a wave.

Live-action shots of mosquitos getting blasted by raindrops.

The authors hypothesized that the reason for minimal momentum transfer is the small mass of mosquitos. In collisions, the transfer of momentum depends on the masses and velocities of the objects. To test this, they created Styrofoam spheres to mimic the raindrops and mosquitos (since, in physics, everything is easier to represent with a sphere), then studied collisions for a wide range of speeds and mass ratios.

They found that the collisions are inelastic—meaning that the drop and insect (or Styrofoam mimics) combine into a larger, slightly slower lump. (Elastic collisions, on the other hand, are like those between billiard balls, where all the kinetic energy is conserved.) Insects or objects with low mass barely impede the raindrop, while a much larger insect (like a dragonfly) would decrease the drop velocity to nearly zero. Following the same logic, the impact force of an inelastic collision decreases with insect size.

The acceleration caused by direct impacts appears to be high: 100–300 g, or the equivalent of 50–150 mosquito weights. By comparison, a typical human can only withstand a downward acceleration of 2–3 g, or up to about 5g upward—although trained pilots and astronauts can increase this. However, the actual force of this acceleration is low, due to the small mass of the mosquito: around 0.6g force (600 dynes). The force of an impact on a stiff surface is nearly two orders of magnitude higher.

The team also performed compression tests using a micromanipulator to determine just how much force a mosquito could withstand and still be able to fly. They found that, thanks to their strong exoskeletons, the mosquitos could survive forces over an order of magnitude higher than the ones they experience due to raindrop impacts. (Fortunately, our fingers are capable of delivering blows of this magnitude.)

Up to this point, our knowledge of how insects and birds fly through rain was minimal. Prior studies of larger animals like bats showed that rain doubled the energy expenditure needed to maintain flight. Heavy rain can significantly hinder aircraft flight by reducing lift and increasing both drag and the potential for stall. These new results not only help improve our understanding in this area, but could also be used to help design rain-resistant insect-sized micro air vehicles (MAVs).

Makes me think of a wave pool. Big waves hit me, I get thrown around a little bit, but generally not much worse for wear. Unless there's a wall right behind me, and I get pushed into the wall. That can hurt.

Same idea here - in midair, not so bad for the mosquitos. When they're sitting on the ground, it's more like getting hit by an asteroid..

629 posts | registered Jan 16, 2002

Ars Science Video >

Apollo: The Greatest Leap

In honor of the 50th anniversary of the beginning of the Apollo Program, Ars Technica brings you an in depth look at the Apollo missions through the eyes of the participants.

Apollo: The Greatest Leap

Apollo: The Greatest Leap

In honor of the 50th anniversary of the beginning of the Apollo Program, Ars Technica brings you an in depth look at the Apollo missions through the eyes of the participants.

Kyle Niemeyer
Kyle is a science writer for Ars Technica. He is a postdoctoral scholar at Oregon State University and has a Ph.D. in mechanical engineering from Case Western Reserve University. Kyle's research focuses on combustion modeling. Emailkyleniemeyer.ars@gmail.com//Twitter@kyle_niemeyer

Out of curiosity, is anything we've learned from this directly applicable to airplane design in the near future?

Probably not. From what I understood, its that the mosquitoes are so small and their mass is so low that they don't transfer much of the momentum from the water, whereas a hard surfaced aircraft absorbs all the momentum form a raindrop.

The research was funded by an NSF grant. The goal is to better understand animal locomotion, with the goal of applying what's learned (bio-inspired design).

Another project from the same grant looked at the mechanics of snake motion, and built an all-terrain snake-like search-and-rescue robot that expended less energy than robots designed for similar purposes.

"The acceleration caused by direct impacts appears to be high: 100–300 g, or the equivalent of 50–150 mosquito weights. By comparison, a typical human can only withstand a downward acceleration of 2–3 g, or up to about 5g upward—although trained pilots and astronauts can increase this. "

This has nothing to do with weight difference, but oxygen distribution system of each species. Humans can't handle more than that before passing out for using water as the oxygen distribution system. Enough G:s and the water flows out of/stops flowing to the head. With insect oxygen is distributed with air, even inside the bug.

A high G number makes little difference in the oxygenation of bug brains.

"The acceleration caused by direct impacts appears to be high: 100–300 g, or the equivalent of 50–150 mosquito weights. By comparison, a typical human can only withstand a downward acceleration of 2–3 g, or up to about 5g upward—although trained pilots and astronauts can increase this. "

This has nothing to do with weight difference, but oxygen distribution system of each species. Humans can't handle more than that before passing out for using water as the oxygen distribution system. Enough G:s and the water flows out of/stops flowing to the head. With insect oxygen is distributed with air, even inside the bug.

A high G number makes little difference in the oxygenation of bug brains.

And the pilots and astronauts is helped by special suits and reclined chairs (in the case of astronauts, fully horizontal as forward is up). If too much blood was not as bad as too little (redout) it may have been better to be launched upside down...

"The acceleration caused by direct impacts appears to be high: 100–300 g, or the equivalent of 50–150 mosquito weights. By comparison, a typical human can only withstand a downward acceleration of 2–3 g, or up to about 5g upward—although trained pilots and astronauts can increase this. "

This has nothing to do with weight difference, but oxygen distribution system of each species. Humans can't handle more than that before passing out for using water as the oxygen distribution system. Enough G:s and the water flows out of/stops flowing to the head. With insect oxygen is distributed with air, even inside the bug.

A high G number makes little difference in the oxygenation of bug brains.

Those are apples and oranges comparisons anyway. instantaneous vs sustained Gs. Pilots can pull up to 9g (wearing the speed jeans) for several minutes sustained. Mosquitos are subjected to 100-300g for how many milliseconds? A better comparison would be a human falling from a rooftop. Or the good old car crash analogy. Tens of gs for a few milliseconds. Can't we survive up to 75g?

Stupid little *****. These creatures are an annoyance to the life and food cycle and have NOTHING to do within it. They were the last of the incarnation of annoyances in this planet earth yet....they inhibit super mass resistance, w t f.

So what happens when they get hit by a raindrop while standing on the ground? The article raises the question and then fails to directly answer it. It says a mosquito could survive 10x the impact of an in-flight raindrop collision, and it says that a drop hitting the ground exerts 100x the force, but there's give in the legs of a standing mosquito so it may not take that much force from an impact while standing on the ground.

Isn't evolution wonderful? It seems that these "researchers" must have worked very hard to come up with a proposal to the government for funding (as required by their deans, also dependent on the feds?). Amazing that us taxpayers can happily support such basically useless work. Can you imagine some private corporation supporting such nonsense?

Isn't evolution wonderful? It seems that these "researchers" must have worked very hard to come up with a proposal to the government for funding (as required by their deans, also dependent on the feds?). Amazing that us taxpayers can happily support such basically useless work. Can you imagine some private corporation supporting such nonsense?

egosumliber wrote:

The research was funded by an NSF grant. The goal is to better understand animal locomotion, with the goal of applying what's learned (bio-inspired design).

Another project from the same grant looked at the mechanics of snake motion, and built an all-terrain snake-like search-and-rescue robot that expended less energy than robots designed for similar purposes.

Isn't evolution wonderful? It seems that these "researchers" must have worked very hard to come up with a proposal to the government for funding (as required by their deans, also dependent on the feds?). Amazing that us taxpayers can happily support such basically useless work. Can you imagine some private corporation supporting such nonsense?

In a quick minute of searching, I found an example of the Naval Research Laboratory publishing a paper on the 3D Aerodynamic Mechanisms of Insect Flight.

The difference between private corporations and public entities performing research you deem "useless," is they are under no obligation to publish it if they think it will do them more good as a proprietary edge.

Isn't evolution wonderful? It seems that these "researchers" must have worked very hard to come up with a proposal to the government for funding (as required by their deans, also dependent on the feds?). Amazing that us taxpayers can happily support such basically useless work. Can you imagine some private corporation supporting such nonsense?

The government should be the one to do more radical or low-margin stuff like this. Leave the tried-and-true things to the stock and margin obsessed businessmen that care only about the money, not the good that comes out what they're working with. The government setting up prizes(money) for companies to reach certain goals is the way of go.

NSF, NRL.. both.taxpayer-supported. I looked at your NRL reference. I read the acknowledgments. All support from the government.

It's interesting that when private entities publish their results, or they support non-governmental research by others, they are often criticized for that 'proprietary edge', especially if their results are at odds with the public-funded conclusions. And they have to account for their spending, not to mention make ends meet to stay in business (otherwise known as making a profit).

Federal agencies are obligated to spend all of the money given to them by the end of their fiscal year. Talk about some wasteful projects dreamed up at year-end.... to essentially get rid of those dollars so they won't be "penalized" in the next year. "Why are you asking for more money when you didn't spend what you asked for last year?"

NSF, NRL.. both.taxpayer-supported. I looked at your NRL reference. I read the acknowledgments. All support from the government.

It's interesting that when private entities publish their results, or they support non-governmental research by others, they are often criticized for that 'proprietary edge', especially if their results are at odds with the public-funded conclusions. And they have to account for their spending, not to mention make ends meet to stay in business (otherwise known as making a profit).

Federal agencies are obligated to spend all of the money given to them by the end of their fiscal year. Talk about some wasteful projects dreamed up at year-end.... to essentially get rid of those dollars so they won't be "penalized" in the next year. "Why are you asking for more money when you didn't spend what you asked for last year?"

That's the wonderful thing about state-sponsored research...we get to learn about things that may not have a readily imaginable commercial application until we learn them. Much irony in the fact that you are using a government-funded-turned-commercially-developed invention to post your right-wing drivel.

BTW, businesses make money by increasing revenue, not by making themselves smaller. If you want government to be like a business (I don't, it's government, not a business) then acknowledge the things that idea entails.